Field of the Invention
This invention relates to the treatment of aqueous slurries or pulps of cement copper in order to recover agglomerates of cement copper which are substantially free of water.
Copper is recovered by leaching low grade copper ores and various waste materials containing low amounts of copper, such as tailings from ore concentrating procedures and the stripped overburden from open pit mining. Water is used as a leaching liquid when copper is to be recovered from a sulfide material and dilute sulfuric acid is used as the leaching liquid when copper is to be recovered from an oxide material. The leaching liquid is slowly percolated through a bed of the ore or waste material and soluble salts are dissolved therein. The leaching liquid containing dissolved copper salts flows through the bed by natural drainage and it is collected and fed to a precipitation plant. The dissolved copper content in the leaching liquid is precipitated by contacting the leaching liquid with iron. The precipitated copper is commonly referred to, in the industry, as "cement copper" and that term will be used in the following description. Cement copper usually assays from about 60 to about 90% copper, with the balance being various impurities such as Fe, S, Al.sub.2 O.sub.3 and SiO.sub.2. It is recovered in the form of a thick slurry or pulp, typically containing about 40 wt. % of water and the balance is solids.
Essentially all of the cement copper particles produced in this way have particle sizes such that they will pass through a 100 mesh screen and, usually, 50 wt. % or more of the cement copper particles will pass through a 325 mesh screen. The slurry or pulp of cement copper can be partially dewatered by filtration, but this can be relatively difficult and expensive to perform because of the fine particle size of the cement copper. Dewatering of the cement copper by drying also is difficult because of the tendency of the cement copper to form oxide. Moreover, the prior processes for treating cement copper did not increase the particle size thereof. The small particle size of cement copper can cause problems in feeding the cement copper to the reverberatory or converter furnaces and in operting the furnaces. Thus, it is desired to treat an aqueous slurry or pulp of cement copper in order to recover the cement copper in a better state for use as a feed in the copper smelting and refining process.
It is an object of this invention to provide a process for treating an aqueous cement copper slurry or pulp to obtain substantially dry agglomerates of cement copper which can be charged as a feed to reverberatory furnaces, converters, etc., in a copper smelting and refining process.
It is another object of this invention to provide a modified process in which relatively large-size pellets of cement copper can be formed by pelletizing the cement copper agglomerates.
It is another object of this invention to provide a process, as aforesaid, in which agglomerates or pellets of cement copper can be calcined to increase the green strength thereof.
It is a further object of this invention to provide a process, as aforesaid, which is inexpensive and simple to perform, and which can be performed using conventional, readily available equipment.
The broad process of forming an agglomerated product, such as a pellet or a ball, from a liquid suspension of solid material or materials in a finely divided form has long been known and certain specific processes utilizing the basic concept are set forth in a variety of United States and other patents. Examples of these patents are those to Puddington and Farnand U.S. Pat. No. 3,268,071, Sirianni and Puddington U.S. Pat. No. 3,368,004 and Capes et al. U.S. Pat. No. 3,471,267. Briefly, all three of these patents refer to a procedure wherein the powders are suspended in a first liquid which is lyophobic to said powders, a second or bridging liquid is then added thereto which is chosen or treated so as to be lyophilic to at least certain of said powders and the system is then agitated. This forms the material which is lyophilic to the bridging liquid into a plurality of agglomerates whose size and shape depend on the details of said procedure as same are set forth at length in said patents and to which reference is invited. These procedures may be and are used both for the separation of one of a mixture of solids from such mixture and such is the main purpose of the above-mentioned Puddington U.S. Pat. No. 3,268,071, or they may be and are used where the formation of an agglomerated product is the objective itself of the agglomeration procedure and such is the principal purpose of the other two patents above-named.
The invention provides a process for treating aqueous cement copper slurries or pulps and forming agglomerates of the cement copper particles contained in such slurries or pulps, which comprises the steps of:
a. adding to the aqueous slurry or pulp of cement copper, (i) hydrophobic organic liquid and (ii) liquid conditioner effective to render hydrophobic the surfaces of the cement copper particles, whereby to displace the water from the surfaces of the cement copper particles whereby the cement copper particles are preferentially wetted by the hydrophobic organic liquid and there is formed a two-phase liquid system containing said cement copper particles wetted by the organic liquid phase and the water phase is essentially free of cement copper particles,
b. agitating the two-phase liquid system to effect repeated collisions of said cement copper particles and thereby forming in said system a dispersion in water of agglomerates, said agglomerates consisting essentially of said solid cement copper particles connected by liquid bridges of said hydrophobic organic liquid and said particles having said conditioner adsorbed thereon and wherein said agglomerates may contain some water trapped in the interstitial spaces therein,
c. discontinuing said agitation and separating said agglomerates from the freely drainable water contained in the dispersion obtained in step (b), and
d. then drying said agglomerates and removing as much as possible of said hydrophobic liquid, said conditioner and trapped water therefrom whereby to obtain substantially dry agglomerates.
According to a second embodiment of the invention, there is provided a process which comprises the steps (a), (b), (c) and (d), as set forth above, followed by the steps of
e. suspending said agglomerates obtained in step (d) in an additional quantity of hydrophobic organic suspending liquid, adding a binding agent for said agglomerates and an aqueous bridging liquid thereto, whereby to displace said hydrophobic organic suspending liquid from the surfaces of said agglomerates and the surfaces of said agglomerates are wetted with said aqueous bridging liquid containing said binding agent whereby to form a two-phase liquid system in which said agglomerates and binding agent are wetted by aqueous bridging liquid phase and said hydrophobic organic suspending liquid is essentially free of agglomerates and binding agent, and agitating the latter two-phase liquid system to effect repeated collisions of said agglomerates and thereby forming a dispersion of pellets in said hydrophobic organic suspending liquid wherein the pellets consist essentially of agglomerates connected by liquid bridges of water and said pellets are impregnated and/or coated with and bound together by said binding agent,
f. discontinuing the agitation and separating the pellets from the freely drainable hydrophobic organic liquid contained in the dispersion obtained in step (e), and
g. then drying said pellets and removing as much as possible of residual hydrophobic organic suspending liquid and water therefrom whereby to obtain substantially dry pellets of cement copper.
According to a further modification of the invention, the agglomerates obtained in step (d) or the pellets obtained in step (g) can be calcined to remove residual volatile matter contained therein and to increase the strength thereof.
Inasmuch as the present invention can make use of well-known equipment, the details of suitable equipment are not disclosed herein. Reference may be made to the three patents noted above, particularly U.S. Pat. Nos. 3,368,004 and 3,471,267 for further details concerning useful equipment and details of agglomeration procedures.